Most industries are presently faced with significant waste disposal problems. As the world becomes more ecologically aware and as governments enact stricter environmental laws, the need for simple, efficient and effective methods for treating waste will increase.
Of particular concern in the area of industrial waste management is the treatment of wastewater. An additional, related concern to the treatment of wastewater is the subsequent treatment and disposal of the solid wastes generated from wastewater treatment processes.
I. Wastewater Treatment
On-site wastewater treatment processes are especially needed in light of the volume and mobility of this form of waste as well as the enactment of stricter regulatory laws. For example, Congress recently enacted the Clean Water Act (CWA-PL92-500), which established a framework for the discharge of treated wastewater to the waters of the United States. One of the provisions of this law levies a $25,000 per day per waste constituent fine against violators. Provisions of the Clean Water Act have also recently been expanded to cover both point and non-point discharges to the waters of the United States.
The provisions of the non-point regulations address the concerns of mixing industrial wastewater with storm water runoff. Two industries particularly impacted by these recent enactments to the Clean Water Act are the transportation and construction industries. Transportation industries must now control incidental losses of oil and grease from vehicle operation. Construction industries must now control the content and turbidity of their storm water runoff.
The marine cargo container maintenance industry has been significantly impacted by these changes to the Clean Water Act. The fact is that most companies in this industry currently violate the Clean Water Act by their uncontrolled discharge of untreated water. Under current industry practice, the untreated water generated from cleaning marine containers is presently allowed to drain to the ground after washing. This wastewater eventually mingles with storm water when rain occurs. This results in a violation of the Clean Water Act whenever there is rainwater runoff.
In order to enable better on-site wastewater management and to assist companies in complying with the Clean Water Act, a simple, efficient, and economical on-site device and process for treating and recycling wastewater is needed.
Wastewater is heavy and therefore costly to transport to off-site water treatment facilities. Further, given storage constraints, wastewater treatment will generally be required frequently. Therefore, it is important that wastewater treatment systems be simple to operate so as to enable those relatively unskilled in the art of wastewater treatment to practice the wastewater treatment process on-site. Simplicity of operation is also an important factor for keeping the cost of water treatment to a minimum.
Water recycling systems also require that there be interim wastewater storage. In order to minimize the capital costs associated with the interim storage facility, the water purification system must be capable of processing large amounts of water rapidly.
Another area of concern regarding wastewater treatment is the minimization of the total volume of wastewater generated. In some areas, water is scarce and/or expensive. In such areas, it is particularly desireable to minimize the volume of water employed. In addition, the cost of wastewater disposal is increasing rapidly everywhere. A purification system that recycles wastewater has the further advantage of minimizing the total volume of wastewater that is ultimately generated. Volume minimization also serves to facilitate the containment and isolation of the waste contaminants. Thus, a closed loop process capable of recycling one batch of wastewater over and over again is particularly desirable.
Numerous methods have been developed for the removal of wastes from wastewater. For example, agents have been added to wastewater that chemically react with the contaminants. Chemical processes often have the disadvantages of being time consuming and requiring complex reaction installations resulting in considerable capital costs. In addition, chemical methods commonly cause the formation of gaseous wastes that also require proper disposal.
One area of particular concern regarding wastewater treatment is the removal of heavy metals from wastewater. Heavy metals, such as copper, iron, silver, zinc, nickel, lead, cadmium and chromium pose severe health and environmental dangers due to the high toxicity of these metals. Zeolites (Perman, U.S. Pat. No. 5,071,587) and anionic polyelectrolytes (Monick, et al., U.S. Pat. No. 4,765,908) have been used to remove heavy metals from wastewater solutions.
Water evaporation processes that yield a concentrated composition of waste contaminants have also been employed as a purification method. Water. evaporation has the disadvantage that it is energy intensive thus rendering this method of purification economically impractical. In addition, evaporation methodologies are not resource efficient where water is expensive and/or in short supply.
Fine suspended waste particles are commonly removed by chemical flocculating agents capable of binding to these waste particles. Iron-II salts, aluminum sulfate, calcium hydrate compositions and lime or sodium aluminate with activated silicic acid compositions are commonly employed as chemical flocculation agents. Chemical flocculating agents can be deficient in the sense that they do not effectively remove solubilized waste components.
Additional water purification methods include those methods that cause thermal, electrical and mechanical decomposition of the waste contaminants.
II. Treatment and Disposal of Wastes Generated From Water Treatment Processes
A further concern regarding the treatment of wastewater is the subsequent treatment and disposal of the solid wastes generated by water treatment processes.
Currently, companies engaging in on-site wastewater treatment are forced to transport the waste generated off-site for further dewatering in order to comply with state standards. For example, in California, the Water Resources Control Board requires sludge to be dried to below a 50 percent water content before it can be disposed of in a landfill. On-site mechanical dewatering, generally, cannot achieve this level of drying.
On-site mechanical dewatering is currently done by mechanically pressing or squeezing the water out of the sludge. Presently, this mechanical process can only lower the water content to 60-70%. In addition, once dried, the sludge must be stored in a dry environment in order to prevent the reabsorption of water until it can be transported for further processing. In light of the current need to ship partially dried solids off-site for further dewatering, existing "on-site" wastewater treatment facilities cannot be said to be completely "on-site."
In addition to being unable to yield a final disposable solid waste, current dewatering methods are labor intensive, cost inefficient and environmentally insensitive. In addition, substantial capital costs are required for both dewatering and storage.
The present need to transport wastes off-site for additional dewatering further increases already significant water treatment costs. The water content of the sludge needlessly escalates already high transportation costs. Thus, an on-site means for achieving drier sludge, even if that drier sludge required further processing, would reduce the costs of solid waste disposal. Furthermore, it is environmentally wasteful to transport overly wet sludge. As energy costs increase, current methods of solid waste disposal become increasingly impractical. Thus, a significant need exists for an improved method for on-site dewatering of solid wastes.